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Is Pluto a Planet?

Arjun Kulkarni Sep 30, 2018
While most people have grown up with the knowledge that there are 9 planets in the solar system, we suddenly find that our textbooks fall 1 planet short, with eight planets.
There were supposed to be 9 planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
There were also various other celestial bodies including asteroids which formed the asteroid belt that lay between the planet Mars and Jupiter and the various 'moons' which were pulled by the gravitational pull of each planet.
And of course the Sun, which ran the whole show, apart from being the protagonist of what we call the Solar System. But recently, there was some kind of convention on our humble planet that felt that Pluto didn't quite make the grade as a 'planet' and stripped it of its status.

The Existence of Pluto

Pluto or 134340 Pluto as it was formally known, was first discovered in 1930.
It was instantly accorded the status of a planet, as it was orbiting the sun. Later a group of experts in the field of astronomy started questioning the correctness of labeling it as a planet.
In the 1970s, astronomers started finding more celestial bodies beyond Pluto, notably 2060 Chiron (not to be confused with Pluto's moon Charon), which fueled a debate for the first time about the inadequacy of Pluto to be called a planet.
The topic went hot and cold for a few years till in 2006, a convention of the International Astronomical Union (IAU) decided that there should be a formal definition for the word 'planet'. To be a planet, a celestial body ought to be able to possess certain characteristics.
Unfortunately for Pluto, it did not get the pass marks in all the required criteria and hence was relegated to being a 'dwarf planet'.
The criteria that the IAU wanted every celestial body to meet were.
  1. The body must have its orbit around the Sun.
  2. It should be spherical by the merit of its own gravitational force. Meaning, its gravity should be able to pull itself into a shape which is spherical.
  3. It should be the biggest, most gravitationally dominant planet in its own orbit.
The IAU ruled that Pluto doesn't qualify the third criterion and it does not qualify as a planet. What followed was a rebuttal by the scientists that believed Pluto to indeed be a planet.

Confusion, Controversy and New Horizons

The reaction against the definition that the IAU set up for a body to be a planet was an immediate claim as it to be flawed, by a large number of scientists.
A few important points in their dismissal for the IAU rules are:

One reason Pluto cannot 'clear its own neighborhood' is because every 228 years, Pluto crosses the inside orbit of Neptune. Now, since it cannot 'clear' Neptune out of its neighborhood, neither can Neptune clear Pluto out of its own, therefore demoting Neptune as a non-planetary body too.
Again, if the same definition was applied to Earth, our planet the Sun along with the asteroid belt and hence cannot clear its own neighborhood either.

Again, this definition was applied only to planets in our solar system, making it a rather flimsy definition since it can't be applied universally.
Another matter that simply could not be ignored was the actual number of votes that passed the decision of Pluto being a dwarf planet. It was a two-week conference, in which the final votes were rushed on the last day with a large number of scientists that contested the definition being absent.
With absentee voting disallowed, the issue became political rather than scientific. The voting still ended with a 4% of the total votes in favor of demoting Pluto. Due to this, the media showed that Pluto was voted off the planet list.
One more thing to note is that even if Pluto was regarded as a 'dwarf planet', it was still a planet nonetheless. Just like dwarf stars are still stars and dwarf galaxies are still galaxies.
The following discussions led by Dr. Alan Stern proposed a broader definition for planets. If accepted, our solar system would then have 13 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.

(A special thanks to Laurel Kornfeld for her inputs into the subject)
The confusion was further fueled by state governments in the United States. Illinois and New Mexico in particular seem to be completely fine with denouncing the ruling of a worldwide body of astronomers and wish that Pluto be given back its planet status.
They believe that there is a sentimental value attached among the people who grew up learning that Pluto is a planet and it is unduly harsh to strip a planet of its status in such a way. They also claim that not all the members were present at the meeting which ruled that Pluto is no longer a planet so justice has not been done to the now dwarf planet.
Not to mention that they do not want Clyde W. Tombaugh, a resident of both these states, to be known by posterity as someone who found what is 'just' a dwarf planet. To this day, these two states insist on celebrating March 13, as 'Pluto Planet Day'.
Optimistic that their photos will unveil new grounds to hopefully conclude this argument, NASA sent their shuttle 'New Horizons' to comprehensive images of Pluto's surface.
The project should yield results when New Horizons reaches Pluto by 2015. This only goes to show that no matter what happens, Pluto will continue to inspire and intrigue scientists of the present and the future.
There are two ways to look it: accept IAU's decision and consider Pluto to be a dwarf planet or to acknowledge the work done by a large number of scientists globally that still consider Pluto to be a planet. It has been more than 80 years since Clyde W. Tombaugh discovered Pluto and this planet is definitely an integral part of our solar system.